The present invention is in the field of rotary power units and in particular it is concerned with a radial, positive displacement power unit suitable for use as a fluid displacing device, namely a pump or a compressor, or as an engine.
The term xe2x80x9cpower unitxe2x80x9d as used herein in the specification and claims is used to collectively refer to pumps, compressors and engines.
Radial power units have long been known. The general configuration with radial power units is a common shaft and one or more radially displaceable pistons adapted for performing pumping or compressing work or for generating work in case of an engine.
Among the advantages of radial power units is the essentially high volume stroke of the pistons within a relatively compact space. Furthermore, radial power units typically generate low noise level and require less maintenance than otherwise configured power units.
Many of the heretofore known rotary power units, in particular pumps and compressors, comprise an eccentric shaft engageable with one or more radially displaceable pistons. A drawback of this arrangement is that the development of undesired forces in the system, resulting in low performance of the power unit. Even more so, where eccentric assemblies are used, there is need to provide some balancing means in order to reduce forces developing in the system, which apart from increasing wear of the system, they might eventually lead to rupture of essential components of the unit.
Furthermore, prior art power units are typically of complex structure rendering them both non compact in size, heavy and being complex in their assembly. In addition, frequent maintenance is required owing to high wear of components and to lubrication requirements.
Still a disadvantage of prior art is the necessity of providing some speed reducing means intermediate a pump or compressor and an engine supplying rotary motion thereto. This arrangement obviously requires more space, is heavier and requires more maintenance.
A considerable disadvantage of prior art is low efficiency wherein essentially high rotational speed is required for delivering sufficient power or pumping/compressing volume, this owing mainly to a small ratio of piston diameter versus stroke.
Another disadvantage of prior art power units is the necessity to provide lubrication which in itself requires special circulation means, frequent servicing and there is always a possibility of lubricant entering the fluid being pumped or compressed. Power units in which lubrication is required, are typically not suitable for supplying gasses for critical applications such as supply of compressed gasses, e.g. oxygen for medical purposes, or other gasses, e.g. for diving or welding or for other industrial purposes.
Typically, a power unit is designed for a particular purpose such as a pump, a compressor or an engine and converting it from one function to another function is either practically impossible or, requires redesigning and changing of most of the essential components of the power unit, rendering it not cost effective. Even more so, a power unit is pre-designed to operate with fixed parameters such as fixed speed, diameter to stroke ratio, etc. These parameters are particularly fixed and are not variable, unless with some considerable modifications in the power unit.
At times, it is desired to increase a working capacity of a power unit, i.e. to increase its volume of fluid displacement in case of a pump or compressor, or to incorporate several power units to operate in conjunction with one another. Prior art power units are not designed to allow stacking of similar such units to one another with complete modularity.
U.S. Pat. No. 2,345,125 discloses a high pressure hydraulic pump in which a central shaft rotates an eccentric octagonal thrust block made of hardened steel, against which a plurality of bronze plunger heads are in sliding contact for displacing of a piston member within a cylinder.
U.S. Pat. No. 4,541,781 discloses a rotary fluid pump comprising rotating rollers running along a circular track for successively depressing a plurality of lever arms which in turn operate pistons in a like number of pumps. In this patent the centrifugal forces developing in the system are used to depress the rollers against the lever arms.
U.S. Pat. No. 5,547,348 discloses a rotor fitted with a primary eccentric rotatable with a shaft and a secondary eccentric adjustable in position relative to the primary eccentric and a plurality of radial piston cartridges are radially disposed around the shaft. This patent discloses stacking of such units however, transferring rotary motion between the stacked units is by a common shaft.
U.S. Pat. No. 5,634,777 discloses a radial piston machine wherein a rotor is formed with a primary eccentric rotatable around an axis and a secondary eccentric adjustable in position relative to the primary eccentric and a plurality of piston cartridges radially disposed around the axis. In this patent sliding friction shoes are provided for contacting the revolving eccentric.
Other prior art patents are U.S. Pat. Nos. 2,789,515, 3,407,707, 3,490,683, 3,871,793, 4,017,220, 5,035,221, 5,281,104, 5,383,770 and 5,547,348.
It is an object of the present invention to provide an improved power unit which, on the one hand, significantly reduces or overcomes the drawbacks of prior art power units and, on the other hand, improves the overall performances of the power unit.
In accordance with the present invention there is provided a rotary power unit, comprising:
a housing having an circular opening and a plurality of bores, each extending along a radial axis from a center of said opening;
a nodular rotor mounted within the opening of the housing and coaxially rotatable within the opening; said nodular rotor comprising a plurality of nodes equally distributed along the bounding circle thereof, the number of nodes being an odd integer less than the number of bores in the housing;
a plurality of replaceable cylinder modules, each fixedly receivable within a respective bore within the housing;
each cylinder module comprising a piston slidable within a cylinder, a piston actuating member associated with each piston and a work unit associated with a cylinder head at a distal end the cylinder; each piston being displaceable along the radial axis between a Top Dead Center (TDC) and a Bottom Dead Center (BDC), the pistons being biased into said BDC;
and wherein the nodular rotor is fitted with a radial thrust reducing arrangement for engagement with respective piston actuating members.
The term xe2x80x9cwork unitxe2x80x9d as used in the specification denotes a unit competent of performing work, e.g. a pumping unit, a compressing unit or a combustion chamber of an engine.
As it will become apparent hereinafter, the rotary power unit in accordance with the present invention significantly reduces wear of its components and consequently reduces maintenance requirements of the components. The power unit provides improved overall efficiency and uses an essentially short stroke versus a large diameter piston with low revolutionary speed on the one hand and, on the other hand, an essentially low linear speed of the pistons with respect to the cylinder wall.
The bottom surface of the piston actuators may be either flat, concave or convex, or may be of a complex shape comprising a combination of flat and arcuate segments. This arrangement is suitable for defining the up-stroke and down-stroke (these terms denote compression/suction displacement of the pistons in case of a pump or compressor or, discharge/intake displacement of the piston in case of an engine). This also permits control of the dwell time at the TDC of the piston which is an important parameter. In accordance with the present invention, within a single power unit, different piston actuators may be used wherein their bottom surfaces are either flat, concave, convex or a complex shape as above.
The dwell angle d of the piston at the BDC, measured in degrees of rotor rotation, is calculated by the formula:
dxe2x89xa7(360xc2x0/n)*0.125 
where:
d is the dwell angle measured in degrees; and
n is the number of nodes.
In accordance with the present invention, the piston is at the TDC when a corresponding node of the nodular rotor extends along the respective radial axis; and the piston is at its BDC when the respective node is angularly displaced by (180xc2x0/n)-d/2 from said radial axis;
wherein:
nxe2x80x94is the number of nodes of the modular rotor; and
dxe2x80x94is the dwell angle between neighboring cylinders (measured in degrees).
In accordance with one embodiment of the present invention, the nodular rotor is associated with a shaft extending from the center of and perpendicular to the plane of the nodular rotor and adapted for receiving or imparting rotary motion to or from the nodular rotor, alternatively. However, the nodular rotor may be driven by a shaft extending into the housing or, in case of several housings stacked on top of one another, the nodular rotor may be rotated by coupling means adapted for simultaneous rotation of the nodular rotors.
In accordance with one aspect of the invention, the work unit is an assembly comprising one or more inlet valves and one or more outlet valves, and wherein rotary motion is imparted to the nodular rotor entailing radial displacement of the piston, thereby establishing a pump or compressor.
In accordance with another aspect of the present invention the work unit is an assembly comprising a fuel supply nozzle, ignition and ignition timing arrangements, and gas exchange passages; wherein radial displacement of the pistons imparts rotary motion to the nodular rotor, thereby establishing a radial engine.
There may also be a combined version of the above aspects, wherein the work unit of some of the cylinder modules is an assembly comprising one or more inlet valves and one or more outlet valves; and the work unit of the remaining cylinder modules is an assembly comprising a fuel supply nozzle, an ignition member and gas exchange passages.
In accordance with a most preferred embodiment, the nodular rotor is associated with a speed reducing assembly. In accordance, with one application, the speed reducing assembly is a planetary gear train, said planetary gear train comprising a sun gear fixed to the shaft, at least one planet gear rotatably supported by the housing, and a ring gear associated with the nodular rotor. In accordance with a different application, the speed reducing assembly is a planetary gear train, said planetary gear train comprising a sun gear fixed to the shaft, at least one planet gear rotatably fixed to the nodular rotor, and a ring gear fixed to the housing.
The piston actuating member may be integral with or rigidly fixed to the piston, with a bottom surface of the piston actuating member adapted for engagement with the nodes of the nodular rotor. The radial distance between the piston and the piston actuator is preferable adjustable, thereby entailing adjusting the clearance of the piston within the cylinder.
In order to reduce wear of mechanical components, to ensure smooth, quiet and efficient performance of the power unit, there is provided a radial thrust reducing arrangement which in accordance with one embodiment is a roller fitted at each node, each roller being rotatable about an axle parallel to an axis of rotation of the nodular rotor.
In accordance with a preferred embodiment, the radial thrust reducing arrangement is a roller having a geared portion fitted on each node for engagement with a geared ring fixed within the opening of the housing, thus imparting the rollers positive rotation about their longitudinal axis. In accordance with this embodiment, the rollers are continuously rotated about their axis and thus as they engage the bottom surface of the piston actuating member, they continue rolling, eliminating radial thrust.
For improved efficiency of the power unit, the cylinder modules are rotationally restrained within their bores. Furthermore, sealing rings are provided on the pistons and still preferably, rider rings are provided on the actuating member slidable within the cylinder module.
In accordance with one embodiment, there is provided a multiple power unit wherein the opening within the housing comprises a plurality of bores arranged in two or more parallel planes; each bore extending along a radial axis from said opening.
Alternatively, two or more housings are coaxially stacked on top of one another in parallel planes, whereby rotary motion is transferred between nodular rotors of neighboring housings.
Where the rotary power unit comprises more than two planes of cylinders, then it is desired that the centers of bores in one plane are angularly offset with respect to centers of bores in a neighboring plane by xcex1xc2x0, wherein xcex1 is derived out of the formula:
xcex1xc2x0xe2x95x90(360/N)/p 
wherein:
xcex1 is measured in degrees;
N is the number of cylinders in each plane; and
P is the number of planes.
When the bores are angularly offset, as above, then continuous, sequential pumping or compressing effect is obtained.
In accordance with a different arrangement, one or more planes of a multi-stage rotary power unit are dedicated to establishing a pump or compressor, and one or more other planes are dedicated to establish a radial engine. However, there may also be provided an arrangement wherein some of the bores comprise one or more inlet valves and one or more outlet valves, and remaining bores are fitted with a fuel supply nozzle, ignition and ignition timing arrangements, and gas exchange passages, whereby a combined radial engine and a pump or compressor is established.
An important character of the power unit in accordance with the present invention is that the nodular rotor is adapted for both clockwise and counter-clockwise rotation and no particular adapting procedure is required. Accordingly, at any stage the nodular rotor may be reversed in direction or rotation.
In accordance with some preferred configurations, the curvature ratio between the diameter of the opening in the housing and a theoretical spherical diameter of the convex or the concave surface is in the order of about 1:1 to about 1:4. Still preferably the piston has a diameter to stroke ratio being greater than or equal to about 5:1 and where the nodular rotor is rotated at about 300 RPM, or less.